Ignorance is indeed frustrating, but it's not a sign of failure. It's just the way it is. We're ignorant of lots of things and we'll continue to be.
But remember, the Big Bang didn't really start to get sketched out in detail until the 1920s and 1930s (hmmmm... productive years in economics too, right?), and really didn't get widely accepted and cleaned up until the 1960s. This was around the time that we really started working out the details of monetary and fiscal stimulus and cleaning up the oversights of the 1920s and 1930s ourselves.
Physics envy is a really ugly thing to see among economists. There's nothing shameful or unscientific about our uncertainty. This is how science progresses, and those physicists we often hold up as paragons of science are dealing with it just like the rest of us are.
UPDATE: Let me clarify that a little. The Big Bang Theory was "widely accepted" before the 1960s, but it was not as near universally accepted as it would be in the 60s and 70s. Steady state models still had a lot of adherents too, and that question wasn't put to rest until the 60s. But it was definitely "widely" accepted before then.